چکیده انگلیسی

Background
Depression is associated with deficits in cognitive flexibility. The role of general slowing in modulating more specific cognitive deficits is however unclear.
Aim
We assessed how depression affects the capacity to strategically adapt behavior between harsh and prudent response modalities and how general and specific processes may contribute to performance deficits.
Methods
Patients suffering from major depression and age- and education-matched healthy controls were asked to randomly stress either speed or accuracy during perceptual decision-making.
Results
Diffusion models showed that patients with depression kept using a less conservative strategy after a trial with speed vs. accuracy instructions. Additionally, the depression group showed a slower rate of evidence accumulation as indicated by a generally lower drift rate.
Conclusions
These data demonstrate that less efficient strategic regulation of behavior in depression is due not only to general slowing, but also to more specific deficits, such as a rigid dependence on past contextual instructions. Future studies should investigate the neuro-anatomical basis of this deficit.

مقدمه انگلیسی

Depression is a major psychiatric disorder, which is usually accompanied by deficits in cognitive functioning, including impairments in cognitive flexibility (Airaksinen et al., 2004, Meiran et al., 2011 and Whitmer and Banich, 2007). In particular, Whitmer and Banich (2007), by using a task-switching paradigm, showed that depressive rumination is associated with deficits in inhibiting previous mental sets. Moreover, patients with major depression show significant deficits when performing the Wisconsin Card Sorting Test (WCST), a test of cognitive flexibility, including problems in shifting cognitive sets when appropriate (e.g., Franke et al., 1993 and Merriam et al., 1999). Perseverative responses and other deficits in the WCST are predicted by the severity of depressive symptoms independently of general intellectual abilities (Martin et al., 1991).
Cognitive flexibility deficits are possibly mediated by prefrontal serotonin deficiency (Clarke et al., 2004). From the functional-anatomical point of view, the dorsolateral prefrontal cortex (especially on the left hemisphere), which is reliably activated during tasks tapping cognitive flexibility (Kim et al., 2011 and Vallesi, 2012), has been shown to be hypo-metabolic in depression (Bench et al., 1992, Davidson et al., 2002, Drevets, 2000 and Mayberg et al., 1999), although many fMRI studies have shown that this region may be inefficiently hyper-active during task execution (see Graham et al., 2013; for a recent meta-analysis). Depression is also accompanied by an abnormal pattern of activation of medial prefrontal structures such as the anterior cingulate cortex (Bench et al., 1992, Diener et al., 2012, Drevets et al., 1992 and Kennedy et al., 2001), a region implicated in energization, drive, and in the effortful allocation of cognitive and motor control (Paus, 2001, Shenhav et al., 2013, Stuss, 2011 and Vallesi, 2012).
The prediction follows that patients suffering from major depression will show impairment in flexible regulation of behavior, especially in tasks recruiting the dorsolateral prefrontal cortex and the anterior cingulate cortex. Cognitive flexibility is for instance required when trading off speed and accuracy. This capacity is important in everyday life because it allows us to flexibly adapt to different and quickly changing environmental and endogenous demands. It has been shown that switching from speed to accuracy by adopting stricter criteria for decision-making involves the left dorsolateral prefrontal cortex (Vallesi et al., 2012). Patients suffering from depression are thus expected to be impaired in this condition. A second prediction concerns possible deficits in the energization process based on anterior cingulate cortex, which should produce generally slower responding (Stuss et al., 2005).
Although a neuroimaging study should be set up to directly test the link between the involvement of these key regions and cognitive flexibility problems in depression, the present study aimed at finding behavioral evidence for deficits in speed-accuracy strategy regulations in major depression. A perceptual decision-making task was adopted in which speed and accuracy instructions were manipulated on a trial-by-trial basis to understand whether depression is associated with cognitive flexibility deficits in trials that require a switch in response strategy, and in slow response patterns especially in trial sequences with high time pressure. To gain deep insights on the possible mechanisms of depression-related deficits in speed-accuracy trade off regulation, we adopted a diffusion model analysis (e.g., Ratcliff, 1978 and Voss and Voss, 2007) of the performance data (i.e., response times and accuracy), which allowed us to estimate more informative decisional and non-decisional sub-processes.